Microelectronic fabrication technology is an extremely diverse field, ranging from the fabrication of discrete custom-made components to on-chip digital/analog circuits with their associated higher-level packaging. However, most of the devices that form the basis of modern microelectronics are fabricated using a single basic approach, namely, by application of UV optical photolithography whereby a pattern is transferred from a “mask” (template) to a photosensitive polymer (photoresist). Once the pattern is developed in the photoresist, it can be used to allow selective deposition, etching or implantation of materials into or over the supporting substrate.
The key disadvantage of this technology is that roughly all the devices are created within a single plane and are surrounded by a supporting material, i.e., the substrate. Thus, the current technology is two-dimensional in nature, and results in many limitations on performance. For example, the source/drain capacitance limits the switching speed in a transistor. This capacitance can be eliminated by designing the transistor in three dimensions. Another limitation that can be eased by three-dimensional device design is heat dissipation. The thermophysical properties of the substrate in two-dimensional structures limit the rate at which heat can be dissipated from a device, which, in turn, limits the amount of current a device can control. Using 3-D wires as the collector, emitter and base, for example, 3-D transistors of related solid-state devices can be created. Finally, three-dimensional structures would result in the elimination of field oxide in a metal-oxide-semiconductor (MOS) circuit. Thus, both data electronics and power electronics would benefit from an economical and efficient process of making three-dimensional components.